The overall aim is to understand better why some very-low-birthweight infants (VLBW:<1500 grams at birth) develop along relatively normal trajectories of behavioral/cognitive development whereas others follow markedly aberrant trajectories. Most VLBW infants are born at least 10 weeks early and some as early as 16 weeks, many experience neonatal medical complications that place their rapidly developing central nervous systems at risk. To understand variations within this population, we focus upon four key factors: (1) variations among these infants in perinatal biological risk; (2) the different early behavioral characteristics associated with higher vs. lower biological risk; (3) the impact of these behavioral characteristics upon how parents and infants negotiate together the major developmental tasks of infancy; and (4) the specific interactive processes associated with each of these tasks that facilitate mastery of the task and more normative development. 90 infants and their primary caregivers are studied longitudinally through two years of age (30 higher- biological-risk VLBW, 30 lower-risk VLBW, and 30 full-term matched in sex, race, and family background to the VLBW groups). Infants' behavioral characteristics are assessed prior to and near term age using standard protocols of social stimulation like that parents provide, neurobehavioral exams, and observations around the taking of vital signs in the nursing. Mother-infant interaction is observed in the home, as dyads sequentially negotiate the developmental tasks of arousal modulation (birth-4 months), coordinated attention to objects and people (9-15 months), and integrated verbal/nonverbal communication (18-24 months). Infants' mastery of these tasks and their general behavioral characteristics are assessed at the end of each developmental period using standardized test situations. Specific interactive processes facilitative of task mastery are isolated for infants with different early biological/behavioral characteristics. Variations in developmental outcome at 2 years of age are assessed by standard tests of motor, cognitive and language performance, and medical and neurological examinations. These assessments are used to test a developmental model of how infant behavioral characteristics together with key interactive processes mediate between infant perinatal biological risk and the quality of general developmental outcome at 2 years. This model holds potential both for understanding better how biological risk exerts its influence on subsequent development and for understanding the quite different developmental trajectories possible for infants of comparable perinatal biological risk.